Twelve years after the Rwanda genocide, nations still seem unwilling to commit the troops and money that would be needed to stop mass slaughter of civilians, a top U.N. envoy said.

Governments have repeatedly promised "never again" in the years since Holocaust and the 1994 Rwanda killings. Yet while they have gotten better at nurturing peace, they are still reluctant to do much more, said Juan Mendez, the U.N. special adviser on prevention of genocide.

"My sense is there's the same kind of wariness," Mendez told a news conference Friday. "'Let somebody else do it' is still very much in place."

Mendez pointed to the continued violence in Sudan's western Darfur region, labeled by the United Nations as the world's worst humanitarian disaster() The international community and the Sudanese government share blame for the continued unrest, which is only getting worse, Mendez said. Foreign powers haven't followed through on his recommendations, while Sudan has not broken the "cycle of impunity" that perpetuates the killings.

"In effect, for the last two years we have engaged in half measures, and those half measures, one, have not been sufficient to protect and, two, they're showing signs of unraveling," Mendez said.